1. Field of the Invention
A method utilized in a wireless communication system and communication device thereof are provided, and more particularly, to a method of managing timing alignment functionality for multiple component carriers in a wireless communication system and related communication device.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, so that the system structure becomes simple.
According to structure of the LTE system, timing alignment (TA) functionality allows a user equipment (UE) with a component carrier to be synchronized with a serving base station on uplink timing for preventing signals transmitted from the UE from colliding with those sent from other UEs under the coverage of the base station. In the TA functionality, the UE has to maintain a time alignment timer whose running state indicates that uplink transmission is still synchronized. The network can control the TA functionality of the UE with a timing advance command. Detailed operation of the TA functionality can be referred in related specifications, and is not given herein.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO) extension up to 4×4, downlink MIMO extension up to 4×4, relaying, and etc.
Based on a concept of bandwidth extension, carrier aggregation is introduced to the LTE-Advanced for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths e.g. up to 100 MHz and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, wherein a UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting on each component carrier. Each component carrier includes a hybrid automatic repeat request (HARQ) entity and a transport block.
However, in the LTE system, each UE is only allowed to use a single component carrier, so the UE maintains synchronization with a base station during TA functionality performance only on the single component carrier. Furthermore, the UE is allowed to connect to multiple component carriers according to the LTE Advancement. However, the LTE Advancement does not clearly specify how the TA functionality is applied in the UE with multiple component carriers. The management of TA functionality for the multiple component carriers is never concerned. Improper configuration on TA functionality with multiple component carriers causes failure of UE synchronization and uplink transmission.
The applicant provides an uplink transmission problem as below based on a direct image on a basis of a combination of the prior art LTE and LTE-Advanced system. Consider a scenario that a UE in a RRC (Radio Resource Control) connected mode is configured with two component carriers for uplink transmission from two cells and the UE maintains a time alignment timer for uplink synchronization as specified in the LTE system. The two cells have different timing advance values for the UE. According to the prior art, the UE updates the timing advance according to a received timing advance command. When the UE applies the timing advance to the uplink transmission for both component carriers, the uplink transmission in one component carrier will be successful, but the uplink transmission in the other component carrier will be failed because the timing advance value is correct in the component carrier, but is not correct in the other component carrier.